US patent application no 2003/0052897 describes a method and a device for generating a data structure from at least a plurality of still pictures, said data structure being backward compatible with the DVD-Video standard, and for recording said data structure on a recordable DVD medium.
US2003/0052897 introduces the concept of Picture Unit (PU). This concept is an add-on to the DVD-Video format for the purpose of providing direct picture access. According to US2003/0052897, the Cells of the DVD-Video data structure are divided into so-called “Picture Units” where each Picture Unit contains at least one Video Object Unit (VOBU) containing Video Data representing a photograph. The “Picture Unit” may comprise additional VOBUs containing audio, video or subtitle information that have been combined with said photograph. According to US2003/0052897, the time allotted for displaying a picture is set by adding non-conventional data to the Navigation Pack (NV_PCK) of the Picture Unit (a PU display time parameter and a slide show display time parameter).
These settings can only be used by players that are PU aware, not the conventional players.
According to the DVD-Video specification (paragraph 5.1.1), a VOBU (except the last VOBU of a Cell) represents a presentation period of at least 0.4 second and at most 1.0 second, and the last VOBU of a Cell represents a presentation period of at least 0.4 second and at most 1.2 seconds. With the solution described in US2003/0052897, if conventional players are used, the display duration of a photograph will be limited to the presentation period of the VOBU containing the video data that represent said photograph (except if it is combined with additional VOBUs containing non-video data like audio data). A presentation period of 1 second will generally be regarded as too short for a slide show.